Purpose: :
Fibrosis and extracellular matrix (ECM) deposition is thoughtto play a role in the development of choroidal neovascularization(CNV), though the mechanism responsible for this is unknown.Mast cells (MC) are also associated with fibrosis but theirrole in CNV in not known. Based on our finding that MCs area source of renin, the rate-limiting enzyme in angiotensin (ANGII) formation, we hypothesized that MC mediators promote fibrosisand dysfunctional ECM synthesis in CNV.

Methods: :
CNV was induced in C57BL/6 mice by laser photocoagulation andeyes were collected at days 3 and 5 post-laser. MC and fibroblast(FB) infiltration was evaluated by immunohistochemistry in cryosections.MCs were stained with avidin conjugated to fluorescein and FBswith an antibody against prolyl-4-hydroxylase, an enzyme involvedin collagen production. To study MC mediators on FB proliferationand collagen synthesis, isolated rodent FBs were grown to confluenceand exposed to ANG II or histamine. FB counts were performedwith a hemacytometer and culture media were assayed for hydroxyprolineand pepsin-soluble collagen.

Results: :
MCs could be identified in the choroid but not in the retinalpigment epithelium layer nor in the retinal layers of non-laseredcontrol eyes and of eyes 3 days post laser. MCs infiltratedthe sites of laser injury and surrounding retina as early asday 5 after laser. MC infiltration seen at day 5 correlatedwith FB activation at the sites of laser injury. Exposure ofisolated FBs to ANG II or histamine caused significant proliferationby 148% and 257% respectively (p<0.05). Proliferation wasinhibited by the selective ANG II AT1R blocker, EXP3174 by 37%(p<0.05) or pyrilamine, a histamine H1R blocker by 60% (p<0.05).Exposure of FBs to ANG II or histamine increased collagen by52% and 99% (p<0.001) and hydroxyproline by 90% and 80% respectively(p<0.05).

Conclusions: :
These data suggest that MCs may play a role in the early stagesof laser induced CNV working in tandem with FBs to promote pathologicdeposition of collagen.